This testimony concerns data from NIOSH which indicate that the ambient carbon-monoxide (630080) levels in mines with diesel or electric equipment are almost always less than 10 parts per million (ppm) and that a carbon-monoxide system capable of detecting a 5ppm increase would be useful as an early warning system for fires. NIOSH would strongly recommend that this provision apply to all belt haulageways, trolley haulageways, or airways containing major electrical or mechanical installations being used to supply air to a work area in underground coal mines. Limiting the carbon-monoxide fire system only to mines using belt haulages for intake air would deprive other miners of an important safety benefit. Also discussed in this testimony are the continued use of electrical power for up to 30 minutes in the event of a mine fan shutdown, the relaxation of some of the requirements in the current standard, the mean entry air velocity, air quality, atmospheric monitoring systems, air quality detectors and air measurement devices, underground electrical installations, and belt conveyor entries.